In recent years, advances in lithography techniques have lead to ongoing, rapid miniaturization of resist patterns. Recently, levels of resolution capable of forming line and space patterns of no more than 100 nm and isolated patterns of no more than 70 nm are being demanded.
In the microprocessing technology used for realizing these high levels of resolution, positive resist compositions that have been proposed as ideal resist materials, particularly for use in methods that include an exposure step using an electron beam, typically employ a polyhydroxystyrene-based resin in which a portion of the hydroxyl groups have been protected with acid dissociable, dissolution inhibiting groups as the base resin. Examples of the most commonly used acid dissociable, dissolution inhibiting groups include so-called acetal groups, such as chain-like ether groups typified by 1-ethoxyethyl groups, and cyclic ether groups typified by tetrahydropyranyl groups, as well as tertiary alkyl groups typified by tert-butyl groups, and tertiary alkoxycarbonyl groups typified by tert-butoxycarbonyl groups (for example, see patent reference 1).
However, in conventional microprocessing technology, the formation of fine patterns with high aspect ratios, and particularly line and space patterns of no more than 100 nm, has proven very difficult due to problems such as pattern collapse caused by the surface tension of the developing solution.
One possible countermeasure for such pattern collapse involves reducing the thickness of the resist film. However, thin films produced using conventional resist compositions suffer from inadequate dry etching resistance.
In relation to this problem, the inventors of the present invention have reported, in non-patent reference 1, that a resist composition including, as a base resin, a copolymer of hydroxystyrene and styrene that has been protected with adamantoxyethyl groups is capable of forming a thin film, exhibits favorable dry etching resistance, and is ideal as a resist material for a method that includes an exposure step using an electron beam.
[Patent Reference 1]
Japanese Unexamined Patent Application, First Publication No. 2002-341538
[Non-Patent Reference 1]
Hojo et al., Journal of Photopolymer Science and Technology, Vol. 16, No. 3, pp. 455 to 458, published Jun. 24, 2003)